In order to cope with requirements of miniaturization and/or high density recording with respect to magneto-optical disc in recent years, so called hybrid media each including a recording area and a program area (premastered area) within a single disc surface have been devised at present.
In such hybrid media, the program area is comprised of emboss pits, and the recording area is comprised of wide grooves. At the innermost circumferential portion of each of the hybrid media, lead-in area where TOC information corresponding to table of contents of recorded information is recorded is provided.
The configuration of such hybrid media is adopted in various magneto-optical discs.
Meanwhile, in the magneto-optical disc, the three-beam method is employed as a method of obtaining tracking error signal thereof.
As shown in FIGS. 1 to 3, this three-beam method is a method in which main beam spot B for reading signal and sub-beam spots A, C spaced by a predetermined distance in track width direction before and after the main beam spot B are used to obtain a tracking error signal. In the three-beam method, the state where the main beam spot B is directly above the track T as shown in FIG. 1 is the most preferable state. In this state, areas of the portions where the sub-beam spots A, C cross (are laid across) the track T are the same, resulting in output of 0. Moreover, when the main beam spot B deviates (is shifted) slightly to the left side as shown in FIG. 2, the area of the portion where the sub-beam spot C crosses (is laid across) the track T is greater than that of the sub-beam spot A, resulting in output of positive value. Further, when the main beam spot B deviates (is shifted) slightly to the right side as shown in FIG. 3, the area of the portion where the sub-beam spot A crosses (is laid across) the track T is greater than that of the sub-beam spot C, resulting in output of negative value. In this way, track deviation of the main beam spot B is detected. Thus, correction is implemented in dependency upon output value corresponding thereto.
However, in the case of obtaining a tracking error signal of the hybrid media by the three-beam method, since, in the hybrid media, as described above, the program area is comprised of emboss pits and the recording area is comprised of wide grooves on the disc surface thereof, there is the possibility that phase of the tracking error signal is changed by 180 degrees (rotated) when light spot is passed through the boundary between the program area and the recording area. Accordingly, great acceleration is applied to the optical pick-up at this time, so an object lens (objective) is vibrated in the inner circumferential direction or in the outer circumferential direction by inertia. For this reason, the tracking servo may be in oscillated state. In addition, such vibration would affect the focus servo as well. As a result, response of the focus servo is lowered. Thus, there may take place the worst state where the entirety of the system is stopped. In this case, for recovery (restoration), a certain time is required. When viewed from end user, missing of information would temporarily take place.
Moreover, in the optical disc, so called CLV system is ordinarily employed. For this reason, a rotation synchronizing signal of the optical disc is taken out from signals recorded on the optical disc to control the number of rotations of the spindle (motor) so that the rotation synchronizing signal has a fixed period. This rotation synchronizing signal is ordinarily obtained from Eight to Fourteen Modulation (hereinafter simply referred to as EFM) signal or Address In Pregroove (hereinafter simply referred to as ADIP) signal. However, since EFM signal does not exist at the innermost circumferential portion of the recording area of the hybrid media, there are instances where when light spot enters the recording area, the number of disc rotations is not stabilized even in the state where the tracking servo is stable.
This invention has be proposed in view of actual circumstances as described above, and its object is to provide an optical disc adapted for implementation of such a control to suppress oscillation of the tracking servo which is apt to take place when light spot is passed through the boundary between the program area and the recording area to realize tracking servo stable at all times to prevent temporal missing of information, and to stabilize the number of disc rotations at all times, and a recording and/or reproducing apparatus for such optical disc.